In present-day wireless local area networks, data are transmitted as a sequence of packets, with each packet being preceded by a known preamble to support acquisition at the receiver end. A proper process of data detection requires synchronization of a receiver carrier oscillator and symbols clock oscillator with the corresponding parameters of an incoming signal. Therefore, a first operation of a receiver, along with preamble detection (that is finding of the accurate time position of the preamble and thus the time position of subsequent payload data), includes detection of the carrier phase and symbols timing phase in the received signal as well.
Noise and frequency distortions that affect signal transmission may cause a failure of the preamble detector: a damaged preamble may be not detected (preamble loss) or a burst of noise may be mistaken for a preamble (false preamble) or phases detection may be done with a prohibitive error. Such events violate data transmission, and the probability of their occurrence should be made as small as possible.
The probability of preamble detector failure may be reduced by use of correlation reception concepts, as it is done, for example, in U.S. Pat. No. 7,379,519 and U.S. Pat. No. 7,756,225. In accordance with those patents, correlation between sections of a received signal and sections of a known preamble are calculated, the calculated correlation results are accumulated, and the accumulated values are compared with a predetermined chosen threshold. Surpassing of the accumulated value over the threshold is used as an indicator of the preamble end.
Advances in process technologies and low cost integration solutions over the past 5-6 years have made wireless communication practically feasible at frequencies of 60 GHz and above. This technical progress is reflected in wireless standards development such as IEEE 802.11ad, IEEE 802.15.3c, WirelessHD, ISO/IEC 1315n and others. The united specifications for 60 GHz wireless technology are referred to collectively as the WiGig standard. A distinctive feature of the new frequency range is a severe path loss: it exceeds the path loss in the conventional 5 GHz band by approximately 23 dB. Such environmental conditions make even more urgent the necessity of development of a receiving apparatus with a high degree of noise immunity. At the same time, the rates of data throughput in the above mentioned standards reached the range of 5-7 Gbps. Systems with such high data speed require wide band signal transmission and use of analog to digital converters with the sampling rates on the order of 10-20 GS/s.
Direct processing at sampling rates of 10-20 GS/s requires too much resources for implementation in practice. To overcome this difficulty, decimation is used in an RF demodulator of the wireless receiver, reducing the sampling rate of the signals to be processed and achieving a drop in the size of required resources by the factor of ten and more. In such a situation, the preamble detector described in the above referenced prior art patents may be used as before, however the position of the preamble end may be found with the accuracy only up to the decimated symbols period. The location of the preamble end inside of the period inevitably remains uncertain.
The goal of the present invention is a synchronization device for a wireless receiver that operates at a decimated symbols frequency, and performs not only preamble detection, but also symbols clock phase detection together with carrier phase detection, while enabling the theoretically possible noise immunity